Throughout this specification the use of the word “inventor” in singular form may be taken as reference to one (singular) or all (plural) inventors of the present invention. The inventor has identified the following related art.
In general, the field of haptics relates to the development, testing, and refinement of tactile and force feedback devices and supporting software that permit users to sense, or “feel”, and manipulate virtual objects or an environment with respect to such attributes as shape, weight, surface textures, temperature and so on.
Generally, it may be stated that of the five senses, namely, sight, sound, smell, touch and taste, it is sight, sound and touch that provide the most information about an environment, where the other senses are more subtle.
In humans, tactile sensing is generally achieved by way of receptor cells located near the surface of the skin, the highest density of which may be found in the hands. These receptors can perceive vibrations of up to about 300 Hz. Therefore, in a haptic interface tactile feedback may generally involve relatively high frequency sensations applied in the proximity of the surface of the skin, usually in response to contact, as such, between a user and a virtual object. In contrast, the human sensing of forces may be considered as more kinesthetic in nature, and may ordinarily be achieved by receptors situated deeper in the body. These receptors are located in muscles, tendons and joints and may be stimulated by movement and loading of a user's body parts. The stimulus frequency of these receptors may be much lower, lying in the range of about 0-10 Hz. Accordingly, in a haptic interface force feedback may comprise artificial forces exerted directly onto the user from some external source.
Therefore, it may be considered there are two aspects to the sense of touch; firstly that which provides kinesthetic information and secondly that which provides tactile information. The kinesthetic information that a user perceives about an object are coarse properties such as its position in space, and whether the surfaces are deformable or resilient to touch. Tactile information may be considered to convey the texture or roughness of an object being ‘touched’. It is desirable that both types of ‘touching’ information be used in a realistic haptic interface.
Haptic Interfaces are systems that enable a user to interact with a virtual environment by sensing a user's movements and then relaying this information to the virtual environment. Along side this interaction, sensory feedback is provided to the user which reflects their actions within this environment, and as a result, it is the design of the haptic interface which conveys the level of sensory interactivity between the user and the virtual environment.
A device developed by M.I.T and SensAble Technologies, Inc, is called the PHANToM™ (Personal Haptic Interface Mechanism) interface, which is largely used in the field of computer haptics. The PHANToM™ interface may allow a user to feel the forces of interaction that they would experience by touching a real version of an object with a pencil or the end of their finger.
A majority of haptic devices are desktop devices, such as those sold under the PHANToM™ range including the PHANToM omni™ and PHANToM premium™. Other devices are generally wearable ones such as gloves and haptic body suits and may have high degrees of freedom and consequently are very expensive. Lower cost haptic devices are usually desktop devices as they have less controlled/actuated degrees of freedom (DOF) compared to their total DOF. For example, the PHANToM omni™ has 6 DOF however only 3 of those are actuated and therefore this device is considered to only provide limited interactivity, i.e. sensors are easier and cheaper to install than motors. Accordingly, at present, certain lower cost haptic devices marketed under the PHANToM™ brand exhibit a force feedback which is only available to three degrees of freedom, namely, in the linear dimensions (x, y, z) out of the six complete degrees of freedom.
During the design stage of a haptic interface, one needs to determine the number of sensors and actuators to be used on the interface so that the level of interaction provides for the highest quality force feedback. In existing interface designs, the inventor is witnessing the use of a larger sensor to actuator ratio, which results in a highly interactive dimensional experience, but is reduced in the level of sensory feedback. The introduction of larger sensor numbers is mainly due to the difficulties in designing a completely transparent force feedback system with high degrees of freedom. Another contributor is the low-cost factor to commercial implementation of more sensors over actuators.
Transparency allows a user to feel realistic forces without adjusting to mechanical issues such as backlash and the weight of the interface itself. It is therefore understandable to see higher transparency interfaces in a low-cost commercial system, as it utilises fewer degrees of freedom that provide force feedback. More complex devices and therefore more expensive ones consequently offer less transparency; however provide greater usability for the requirements of rendering and interacting with rich and complex virtual worlds.
The current low-cost interfaces have limitations that have been recognised to provide certain restrictions on the user from interacting with the virtual environment. One of these restrictions is the ability to grasp and manipulate virtual objects with sensory/force feedback. Grasping is one of the most basic abilities of human interaction, yet it has shown to be one of the most difficult to achieve with respect to haptic interface design.
Early attempts at simulating grasping were based on the use of two, three degree of freedom (DOF) devices. While this configuration provides a very realistic simulation, a significant amount of workspace is required, which is very limiting if an attempt is made to utilise a dual-hand approach. There have been several attempts at developing a desktop device which is able to simulate grasping with three dimensional manipulation and force feedback, however the majority of these devices have depicted tools such as laparoscopic or endoscopic tools for minimally invasive surgery. In view of this it would also be desirable to provide a device which is capable of being adapted to different applications.
The interactive performance of the PHANToM™ device relies on a single point of interaction with the virtual or tele-manipulated environment. Attempts have been made to introduce multiple points of interaction through addition of grasping mechanisms with force feedback to a haptic device. This approach allows for the extension of grasping with force feedback, the addition of motion and force feedback with three degrees of freedom. Typically such additions may comprise the drive motor(s) and pulley system(s) required for the gripping function to be included on the end of the haptic device which adds extra weight to the system and results in diminishing overall performance.
One potential solution to the above problem, in relation to a single idealized pair of “soft fingers” (ie a point contact with friction) where no internal torsion is exerted on an object during grasping, is to use a single drive motor and cable pulley system which sits on the end of a haptic device1. A single drive motor and cable pulley system relates to both fingertips in this design as the second fingertip feels the reaction force of the grasped object (it is the same as squeezing a golf ball between a thumb and index finger, the force felt on both fingers is the same). However, it is not clearly evident that the position of the unactuated finger is tracked. Attached to the pulley is a finger interaction point which is driven by a motor and cable system, depending on the appendage that is used to interact with the device, i.e. the thumb or index finger interface. The other finger interface (ie an opposed finger for gripping) is directly coupled to the actuated interface, which means that both fingers will move an equal distance from each other and the haptic device. Consequently, to reduce the weight of the grasping interface, a small drive motor is used and as a result the maximum force of the system is relatively small. This design may limit the finger interfaces by not allowing the user to experience individual external forces applied to each finger. This design may also be limited in that no torque can be exhibited to the user which ultimately limits the interactive experience for a user and the applicability of the device. 1_, K. Salisbury, R. Devengenzo. Toward virtual manipulation: from one point of contact to four. Sensor Review, Vol. 24-Number 1-2004-pp. 51-59.
The aforementioned problems are not intended to be an exhaustive reference, but rather an indication, in the view of the inventor, as to the general weaknesses that current systems have encountered, which tend to weaken the effectiveness of previously developed grasping interfaces.
By way of example, FIG. 1a illustrates a known haptic interface system 1a having a wheeled or tracked platform 2a and a commercially available haptic device 3a such as the above noted PHANToM™ interface. The haptic device 3a has a probe 5a. Inputs to the system 1a in the form of operator hand movements of the probe 5a are translated into control inputs to the platform 2a which are transmitted over the communication channel 4a. Application specific haptic augmentation is in turn transmitted to the operator over channel 6a. 
For example, the operator may control the motion of the platform 2a as it explores a remote environment, aided with images from an on-board camera. When the platform is likely to collide with an obstacle then haptic augmentation in the form of appropriate forces are provided to the operator to indicate to the operator that the robot is about to collide with an obstacle.
The inventor has also identified the following related art. The simulation of motion may be broken down generally into two components, namely, fundamental forces of motion and, the body's sensation or experience during motion. With respect to the first component of fundamental forces of motion, most simulators are more or less stationary and have no momentum therefore they must produce a force that moves a user to simulate a change in direction or momentum for the simulated motion. In general, the fundamental movements of a simulator may be considered as pitch (tilting up or down), roll (sideways rolling to the left or right) and, yaw (turning left or right within a horizontal plane). It is desirable that a sophisticated simulator may also facilitate vertical, lateral and longitudinal displacement, which effectively provides six degrees of freedom to the system. With respect to the second component of the body's sensation of motion, it can be said that this relates to the brain's interpretation of the experience through the bodily senses. The inner ear and vision are considered to play a major role. Sound may also have an influence on the brain's interpretation of motion. Also, touch or tactile sensation may provide a means of establishing an interpreted reality of motion. Tactile sensation is generally provided by motion simulators by way of audio drivers or vibration generators operatively associated with the structure of the simulator itself.
There are several commercial motion simulators available such as flight simulators. An example of simulators are those offered by Moog, Inc and its affiliated companies throughout the world using a hydraulic based servo actuator configured in a closed chain kinematic manner, however, the motion and work envelope of these systems may be very limited. Available simulator technology may use a ‘pod’ as the simulated operator space to represent the physical environment between the operator and the simulated system. In motion enabled simulation systems this pod may be mounted on a motion platform, and visual cues and motion commands may be generated in response to the user's operation of the controls and the simulated system's interaction with the virtual environment.
Most motion simulator systems whether flight, car, tank simulator etc. have one weakness in common. Their lack of full body motions through mechanical constraints, for instance, is still a topic of challenging research for virtual environment technology. In most cases existing technology may use a “cabin” that represents the physical vehicle and its controls. The cabin may be ordinarily mounted on a motion platform, and virtual window displays and motion commands may be generated in response to the user's operation of the controls. These systems also tend to be specialized to a particular application.
In recent years there has also been the exploitation of such technology by the entertainment industry and adventure rides. However, for many kinds of virtual environment applications, more active self-motion may be required. The major challenges for full body motion in a virtual environment arise whenever we have locomotion through a large virtual space, locomotion over varying surface characteristics, and motion in a direction other than horizontal are required. Thus, the replication or simulation of full body motions represents a challenging topic of research in virtual environment technology.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.